In the recent years, a thermally assisted magnetic recording method has been proposed as a recording method to realize a recording density of not less than 1 Tb/in2 (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)). With conventional magnetic recording apparatuses, when the recording density is not less than 1 Tb/in2, there is a problem of disappearance of recorded data due to a thermal fluctuation. It is necessary to increase coercivity of a medium in order to prevent the disappearance; however, because there is a limit in the magnitude of magnetic field that can be generated, it is impossible to form recording bits in the medium when coercivity is increased too much. In order to solve the problem, in the thermally assisted magnetic recording method, the medium is heated by a light at the moment of recording, whereby coercivity is decreased. Herewith, recording on a high coercivity medium is possible, making it possible to realize the recording density of not less than 1 Tb/in2.
In a thermally assisted magnetic recording apparatus, it is necessary to make a spot diameter of a light to be irradiated approximately the same size (a few tens nanometers) as that of the recording bit. Because when the diameter is larger than that, the data of the adjacent truck is deleted. For heating such micro regions, an optical near-field is used. The optical near-field is a localized electromagnetic field present near a micro object which dimension is less than a light wavelength (a light which wave number has imaginary components) and is generated using a small aperture or a metal scatterer with a diameter of less than the light wavelength. For example, in “Technical Digest of 6th international conference on near field optics and related techniques, the Netherlands, Aug. 27-31, 2000, p 55”, an optical near-field generator using a triangular shaped metal scatterer is proposed as a high-efficiency optical near-field generator. When a metal scatterer is illuminated by light, a plasmon is excited within the metal scatterer and a strong optical near-field is generated at the apex of the triangle. The Use of this optical near-field generator makes it possible to gather the light high-efficiently in the region of less than a few tens nanometers.    [Non-patent document 1] Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)    [Non-patent document 2] Technical Digest of 6th international conference on near field optics and related techniques, the Netherlands, Aug. 27-31, 2000, p 55